1. Field of the Invention
The present invention generally relates to controlling a power source of an electronic device, and more particularly to the control of a power source, which allows power consumption of the power source to be reduced while the electronic device is inactivated.
2. Description of the Prior Art
Various electronic devices are supplied with power from a battery or a commercial power source. FIG. 4 shows functional blocks representing the peripheral components surrounding a power source circuit in an electronic device, such as a notebook-sized PC.
In FIG. 4, a functional circuit 10 is provided to accomplish the original function of electronic devices, such as a PC or a cellular phone. The functional circuit 10 receives power from an AC adapter, a battery, or the like via a DC/DC converter 12. The AC adapter refers to a device for converting a power voltage to a predetermined DC voltage. The battery can be various types of batteries, such as a commonly used alkali-manganese battery, a lithium-ion battery, or other batteries. The DC/DC converter 12 converts the received voltage to a proper voltage before supplying it to the functional circuit 10, since the voltage from the AC adapter or battery may be unstable. The DC/DC converter 12 can be omitted if the functional circuit 10 is capable of responding to a wide voltage range.
Whether the DC/DC converter 12 should convert a voltage is controlled by a control circuit 14. The control circuit 14 continuously supervises the output voltage of the AC adapter or battery using voltage sensors 16a, 16b. When the output voltage from the AC adapter or battery exceeds a reference voltage, if a power source is turned on with an external switch 20, then the DC/DC converter 12 is forced to the operating mode to supply power to the functional circuit 10. In the meantime, if the external switch 20 is maneuvered so as to shut off the power supply to the electronic device, the control circuit 14 forces the DC/DC converter 12 to halt its operation and stops supplying power to the functional circuit 10.
When it is judged that both the AC adapter and the battery are used, the control circuit 14 charges the battery on certain conditions. Charging the battery is carried out by a battery control circuit 18. Where both the AC adapter and the battery are used, the control circuit 14 causes the battery control circuit 18 to operate so that part of the power supplied from the AC adapter is returned to charge the battery.
Whether both the AC adapter and the battery are used is checked by the control circuit 14 via the voltage sensors 16a, 16b.
The control circuit 14 is thus playing a major role in supplying power to the functional circuit 10, charging the battery, etc. It should be noted that the control circuit 14 itself receives power from a power circuit 22.
As described above, in the conventional electronic devices including the notebook-sized PC and the cellular phone, the control circuit 14 still operates while the electronic device is inactivated and the DC/DC converter 12 is stopped. This is because the control circuit 14 continuously supervises the connect/disconnect of the AC adapter or the battery, and the turn on/off of the switch 20 as well. Namely, the control circuit 14 consumes power, though it is very little, via the power circuit 22 even when the electronic device is inactivated, and therefore receives power from the AC adapter or the battery.
For example, in a typical notebook-sized PC, the control circuit 14 may consume as much as about 20 mA current via the power circuit 22. As a result, a battery having a 1600 mA capacity would be completely discharged in about three days, even if the notebook-sized PC has not been activated.
Japanese Patent Laid-Open Publication No. Hei 5-241696 discloses an example of a PC which can save the battery depending on the presence or the absence of an AC adapter. Also, Japanese Patent Laid-Open Publication No. Hei 6-83491 discloses a technique for minimizing the overall power consumption of the notebook-sized computer by collecting and interpreting the power-related data for each process element. The technique allows the control of the power supply. Further, Japanese Patent Laid-Open Publication No. Hei 6-161617 discloses a technique for reducing the power consumption of the power supply control device itself.
As described above, there has been a problem in the conventional electronic devices that the battery might be used up only in a few days, even if the power source is turned off, due to the continuous slight power consumption of the electronic device while it is inactivated.